(Abridged) Lunar occultations (LO) are a very efficient and powerful technique, that achieves the best combination of high angular resolution and sensitivity possible today at near-infrared wavelengths. Given that the events are fixed in time, that the sources are occulted randomly, and that the telescope use is minimal, the technique is very well suited for service mode observations. We have established a program of routine LO observations at the VLT observatory, especially designed to take advantage of short breaks available in-between other programs. We have used the ISAAC instrument in burst mode, capable of producing continuous read-outs at millisecond rates on a suitable subwindow. Given the random nature of the source selection, our aim has been primarily the investigation of a large number of stellar sources at the highest angular resolution in order to detect new binaries. Serendipitous results such as resolved sources and detection of circumstellar components were also anticipated. We have recorded the signal from background stars for a few seconds, around the predicted time of occultation by the Moon's dark limb. At millisecond time resolution, a characteristic diffraction pattern can be observed. Patterns for two or more sources superimpose linearly, and this property is used for the detection of binary stars. The detailed analysis of the diffraction fringes can be used to measure specific properties such as the stellar angular size and the presence of extended light sources such as a circumstellar shell. We present a list of 191 stars for which LO data could be recorded and analyzed. Results include the detection of 16 binary and 2 triple stars, all but one of which were previously unknown. The projected angular separations are as small as 4 milliarcseconds and magnitude differences as high as ?K=5.8 mag...
We report the first-time use of the Aqueye+ and Iqueye instruments to record lunar occultation events. High-time resolution recordings in different filters have been acquired for several occultations taken from January 2016 through January 2018 with Aqueye+ at the Copernicus telescope and Iqueye at the Galileo telescope in Asiago, Italy. Light curves with different time bins were calculated in post-processing and analyzed using a least-square model-dependent method. A total of nine occultation light curves were recorded, including one star for which we could measure for the first time the size…
TIRCAM2 is the facility near-infrared Imager at the Devasthal 3.6-m telescope in northern India, equipped with an Aladdin III InSb array detector. We have pioneered the use of TIRCAM2 for very fast photometry, with the aim of recording Lunar Occultations (LO). This mode is now operational and publicly offered. In this paper we describe the relevant instrumental details, we provide references to the LO method and the underlying data analysis procedures, and we list the LO events recorded so far. Among the results, we highlight a few which have led to the measurement of one small-separation bina…
We report on 26 lunar occultation events observed in the context of a program started at Devasthal in 2017. In addition to the customary observations with the 1.3-m telescope, we report here also the first attempts performed with the TIRCAM2 camera at the 3.6-m DOT telescope in the near-IR. The results consist in the first-time angular diameters for two late-type giants, in a measurement of the well-known AGB pulsating variable SW~Vir, and in the measurement of eight small separation binaries one of which is detected for the first time (HR~1860). We also measured the wider binaries SAO~94431 a…
Lunar occultation (LO) technique in the near-infrared provides angular resolution down to milliarcseconds on the occulted source even with ground-based 1m class telescopes. LO observations are limited to brighter objects because they require high signal to noise ratio (S/N ~ 40) for proper extraction of angular diameter values. Hence, methods to improve the S/N ratio by reducing noise using Fourier and Wavelet transforms have been explored in this study. A sample of 54 near-infrared LO light curves observed with IR Camera at Mt Abu observatory has been used. It is seen that both Fourier and Wa…
The uniform disk (UD) angular diameter measurements of two oxygen-rich Mira variables (AW Aur and BS Aur) and three semiregular (SRb) variables (GP Tau, RS Cap, RT Cap), in near Infrared K-band (2.2 micron) by lunar occultation observations are reported. UD angular diameters of the two Miras and one SRV are first time measurements. In addition a method of predicting angular diameters from (V-K) colour is discussed and applied to the five sources. The effect of mass-loss enhancing measured K-band diameters is examined for Miras using (K-[12]) colour excess as an index. In our sample the measure…
We report on 25 sub-arcsecond binaries, detected for the first time by means of lunar occultations in the near-infrared as part of a long-term program using the ISAAC instrument at the ESO Very Large Telescope. The primaries have magnitudes in the range K=3.8 to 10.4, and the companions in the range K=6.4 to 12.1. The magnitude differences have a median value of 2.8, with the largest being 5.4. The projected separations are in the range 6 to 748 milliarcseconds and with a median of 18 milliarcseconds, or about 3 times less than the diffraction limit of the telescope. Among our binary detection…
The recently inaugurated 2.4\,m Thai National Telescope (TNT) is equipped, among other instruments, with the ULTRASPEC low-noise, frame-transfer EMCCD camera. At the end of its first official observing season, we report on the use of this facility to record high time resolution imaging using small detector subarrays with sampling as fast as several $10^2$\,Hz. In particular, we have recorded lunar occultations of several stars which represent the first contribution to this area of research made from South-East Asia with a telescope of this class. Among the results, we discuss an accurate measu…
We report on 13 sub-arcsecond binaries, detected by means of lunar occultations in the near-infrared at the ESO Very Large Telescope. They are all first-time detections, except for the visual binary HD~158122 which we resolved for the first time in the near infrared. The primaries have magnitudes in the range $K$=4.5 to 10.0, and the companions in the range $K$=6.8 to 11.1. The magnitude differences have a median value of 2.4, with the largest being 4.6. The projected separations are in the range 4 to 168 milliarcseconds with a median of 13 milliarcseconds. We discuss and compare our results w…
We have recorded three lunar occultations of Aldebaran (AlfTau) at different telescopes and using various band-passes, from the ultraviolet to the far red. The data have been analyzed using both model-dependent and model-independent methods. The derived uniform-disc angular diameter values have been converted to limb-darkened values using model atmosphere relations, and are found in broad agreement among themselves and with previous literature values. The limb-darkened diameter is about 20.3 milliarcseconds on average . However, we have found indications that the photospheric brightness profil…
We report further results from the program of lunar occultation (LO) observations started at the 2.4-m Thai National Telescope (TNT) in 2014. We have recorded LO events of 18 stellar sources, leading to the detection of four angular diameters and two binary stars. With two exceptions, these are first-time determinations. We could resolve angular diameters as small as 2 milliarcseconds (mas) and projected separations as small as 4mas. We discuss the individual results, in the context of previous observations when available. The first-time angular diameters for o Psc, HR 6196 and 75 Leo are in g…
A study on the contribution of the interplanetary medium in radio occultation experiments
Indian Institute of Technology Indore（印度印多尔理工学院）；Indian Space Research Organization, Vikram Sarabhai Space Centre（印度空间研究组织，维克拉姆·萨拉巴hai航天中心）；ISRO Telemetry Tracking and Command Network（印度空间研究组织遥测跟踪与指令网络）；The University of Tokyo（东京大学）
Lunar occultations (LO) provide a unique combination of high angular resolution and sensitivity at near-infrared wavelenghts. At the ESO Very Large Telescope, it is possible to achieve about 1 milliarcsecond (mas) resolution and detect sources as faint as K$\approx$12\,mag. We have taken advantage of a passage of the Moon over two crowded and reddened regions in the direction of the inner part of the galactic bulge, in order to obtain a high number of occultation light curves over two half nights. Our goal was to detect and characterize new binary systems, and to investigate highly extincted a…
Calibration is one of the long-standing problems in optical interferometric measurements, particularly with long baselines which demand stars with angular sizes on the milliarcsecond scale and no detectable companions. While systems of calibrators have been generally established for the near-infrared in the bright source regime (K$\la 3$\,mag), modern large interferometers are sensitive to significantly fainter magnitudes. We aim at providing a list of sources found unresolved from direct observations with high angular resolution and dynamic range, which can be used to choose interferometric c…
Eclipses by Artificial Satellites to Measure the Angular Sizes of Stars
Durham University（杜伦大学）；University of Toronto（多伦多大学）；University of California, Berkeley（加州大学伯克利分校）；The Hong Kong University of Science and Technology（香港科技大学）；Nazarbayev University（纳扎尔巴耶夫大学）；Université Paris Diderot（巴黎狄德罗大学）；Université de Paris（巴黎大学）；Donostia International Physics Center（多诺斯蒂亚国际物理中心）；University of the Basque Country UPV/EHU（巴斯克大学）
Large-scale Morphology of the Optical F-corona from a Total Solar Eclipse Observation During the Artemis II Lunar Flyby
Tokyo City University（东京都市大学）；Tohoku University（东北大学）；National Astronomical Observatory of Japan（日本国立天文台）；Ishigakijima Astronomical Observatory（石垣岛天文台）
We present models of the inner region of the circumstellar disk of RY Tau which aim to explain our near-infrared ($K$-band: $2.1\,μ$m) interferometric observations while remaining consistent with the optical to near-infrared portions of the spectral energy distribution. Our sub-milliarcsecond resolution CHARA Array observations are supplemented with shorter baseline, archival data from PTI, KI and VLTI/GRAVITY and modeled using an axisymmetric Monte Carlo radiative transfer code. The $K$-band visibilities are well-fit by models incorporating a central star illuminating a disk with an inner edg…
The angular size of a star is a critical factor in determining its basic properties. Direct measurement of stellar angular diameters is difficult: at interstellar distances stars are generally too small to resolve by any individual imaging telescope. This fundamental limitation can be overcome by studying the diffraction pattern in the shadow cast when an asteroid occults a star, but only when the photometric uncertainty is smaller than the noise added by atmospheric scintillation. Atmospheric Cherenkov telescopes used for particle astrophysics observations have not generally been exploited fo…
An amateur astronomer in the modern world has the opportunity not only to make visual observations for own interest, but can make scientific astronomical observations and new discoveries in astronomy. In my example, as amateur astronomer and only through self-education, I inform about my discoveries: of the possible dwarf nova on the old digitized photographic plates and of new variable stars from sky surveys data by means of data mining; how I discovered (in the images of the sky surveys): astronomical transients, supernovae, planetary nebula candidates and new binary systems in the data of G…
